Electrical signal storage



Aug. 13, 1957 F. D. COVELY ET AL ELECTRICAL SIGNAL STORAGE Filed Sept.. 4', 1951 2 Sheets-Sheet 1 BY ZD i ATTORNEY Aug- 13, l957 F. D. covELY ET AL 2,802,957

ELECTRICAL SIGNAL STORAGE Filed Sept. 4, 1951 2 Sheet`s-Sheet 2 ffy-2 V01. T5 mean' 1567/?005 P0 rilVr/HL 77A im@ 2) /V A fee-Aw (2) l%\\\ \y/ W Wie/75(2J Wf/T mme.,

f ATTORNEY JnitedV StatCS 2,802,967 c ELECTRICAL SIGNAL STORAGE Frank D. Covely, Collingswood, N. J., and Richard E. Baker, Indianapolis, Ind., assignors to Radio Corporationof America, a corporation of Delaware Application September 4, 1951, Serial No. 244,912

11 Claims. (ci. 315-22) The present invention is related to the storage of electrical1signals,'and more particularly to the storage of such signals in storage tubes.

It is known to store signals in a storage tube, read the stored signals, and store them again at substantially the echo detection and ranging) or radar systems where long storage times are required. For example, the highest persistence cathode ray tubes used in a PPI (plan position indication) type of system, may be insufficient to allow display ofthe ventire region being surveyed by the radar or sonar set at the desired rate of scan of the region.

The copending application of Frank D. Covely and Richard E. Baker, entitled Electrical Signal Storage, Serial No. 236,442, filed July 12, 1951, discloses an improvement upon the storage systems of the type disclosed above, which allows the use of a single two-gun storage tube. In the said copending application, a system is described inwhich, briey, the reading beam of a twogun storage tube is maintained in advance of the writing beam. 'Ihe `signals read are circulated through a circulating signal loop and reapplied to the writing beam. The lag of the writing beam is such that the signals are rewritten on the same points from which they were originally read.

It is an object of the present invention to provide another improved storage system ofthe type in which signals are circulated and stored again at points corresponding to those from which they were read on a storage tube target.

It is` another object of the invention to improve the registrationof the storage points of the signals circulated and stored again withthe corresponding points from which they were read from a storage tube` target. Another object of theinvention is to provide a system ofthe type described in which only a single single-gun storage tube 'is required, rather thanthose in which a multiple-gun tube or infwhich multiple tubes are required.

In accordancewiththe invention, a storage tube is employed havingfa single electron beam gun. The electronpbeam deilection is modulated to cause the beam alternately toadvance in equal steps and retreat in equal steps across the target in the direction of its sweep, each advance being greater than eachretreat. Thus the beam moves across the,V target, by steps both forward and backward, the formerbeing greater than the latter. The target-p1"V other reading electrode is coupled to aloop circuit whichre-applies the signal read to the writing control electrode of the electron beam gun after a certain delay ice time. The electrodes are modulated so that at each forward step `of the beam across the target a stored signal is read; at each backward step a signal from the loop circuit is written. But the forward and backward steps are correlated with the delay time so that the signal read at one forward step is rewritten on the target, or stored again, when the beam next reaches this point on a backward step. With this system of the invention, more exact registration of the restorage of signals with the points on the targets from which these same signals were read -over` prior methods is achieved. The employment of a single-gun tube makes more precise registration easier to achieve, whereas registration is a diflicult problem when two or more electron beams are employed, one to rewrite or restore the signal read by the other beam.

A further feature of the invention resides in a novel inter-lace scanning scheme, which tends to avoid signal creep. In accordance with this further feature, the forward and backward steps read'and write respectively at intervals of about two beam widths `or element sizes, on one target scan. Thus, the stored signal is circulated only for alternate elements. Signals from the other alternate elements are read, circulated, and restored only on the next frame of the targetscan.

The foregoing objects, and `other objects, advantages, and novel features of the invention will be more apparent from' the following description when taken in connection with the accompanying drawing in which:

Fig. l is a schematic diagram, largely in block form, illustrating onelembodiment of the invention;

Fig. 2 is a set of graphs explaining motion of the beam across a strobe line of the storage target face and useful in understanding the operation of the embodiment of Fig. 1; Fig. 2A is a view of the storage target face showing the strobe line shown separately in Fig. 1 and motion of the beam on the line, although grossly out of scale; and

Fig. 3 is a graph useful in understanding the operation of the invention with the inter-laced scanning mentioned hereinbefore.

Referring to Fig. l, the signals to be stored may be applied between the terminals 10, 12 of a mixing circuit 14 which is to mix incoming signals with those just read, if any. Preferably, for reasons set out hereinafter, a nonadditive mixing circuit is employed. A discussion of such non-additive mixing circuits and their employment may be found in Vacuum Tube Amplifiers, edited by Valley and Wallman, volume 13 of the Radiation Laboratory Series, starting near the bottom of page 100. Another improved form of such a non-additive mixing circuit which may be employed is disclosed in U. S. Patent No. 2,695,953, issued November 30, 1954, to Edwin M. Seabury. The terminal 12 may be connected to a common conductor, conventionally indicated as ground. t

The circulating signal is also applied to the non-additive video mixer 14 at a terminal 16 from a delay line 44 supplied by an erase controlcircuit 46 with signals from a demodulator 18. The .output of the video mixer 14 is applied by connection 20 to a video amplifier 22. A control element 24 of a writing electron gun 26 of a storage tube 28 receives the output of the video amplier 22 after passage of the signal therefrom through a switch 23. Magnetic deection coils 29 as illustrated (or well-known electrostatic deflection plates) provide deection means for the electron beam generated in the gun 26. The gun 26 is schematically shown without any power supplies being illustrated, such power supplies being known. The storage tjube 28 may be of the type sometimes called a barrier-grid storage tube Aorn a Radechon. Such a tube is described inl detail in the RCA Review, volume X, No. 1, pp. 112 through 135 (March 1948)-' l A target 30 of the storage tube receives the electron 22 and stores an electrical charge corresponding to the signal at each point as the beam is swept across the target 30. The target 30 includesra grid 30a arranged in front of and closelyspaced .from a'micalrplate' 3011 andan electrode 30C depqsited` on the side of 'theplate opposite thevgrid. A high frequency oscillator34 having a sine wave output with a frequencyl of the order of 30 mot/js.

(megacycles per second) is also, applied through the switch 23 to the control :element 24 ofthe storage tube 28,.v vA low frequency oscillator V35 (having an output signal the frequency of which may be of the order of 250 to' 500 kc., dependent` upon the radar pulse Vrepetition rate and the resolution required) is connected to the Y kswitch 23,'which switch of course may beV a suitable ground. The inductor V504 is tuned as jbyfits own shuntV capacity to` be parallel Yresonant at 30 mc. /s. The tuned circuit vof the inductor and its capacity is connected at the junction of the inductor 50 andthe capacitor 4,8to an RF. (radio frequency) amplifier 52, the output of which Vsupplies signals to the demodulator 18. The -lowv4 frequency oscillator 35 appliesv voltage through anblock-ing capacitor 54 and a resistor 56 to the electrode 30p. n

The circuit illustrated may be usedin connection with a radio echo detection and ranging systemuSS from which pulses of radion'frequency energy are-emitted from a radiator or receptor 60Aand echoes received at radiator or receptor 60 are demodulated and applied as the video signalsappearing at the terminal 1t) of the video mixer 14.` yThe 4echo detection and ranging system maybe Y either'a radar or a sonar system, the radiator or receptor being respectivelyeither an antenna or a shunt radiator or receptor, as known. A l .A n A trigger signal on connectionl62 issynchronized at a suitable submultiple of the low frequency oscillator 35 by a trigger Vgenerator circuit 64. It is contemplated that the returned signals may be stored and ultimately displayed inthe form of a plan position indicator display on a iinalrdisplay device 66. Y V In operation, the radar system 58 emits a pulse of radio frequency energy at the antenna 60. At the saine 'time the sweep generator 68 receives a trigger signal and applies a sweep voltage to the deflection coils 29 to deflect the electron beam from the gun 26. i The electron beam is thereby deflected, for example, initiating one sweep with each trigger from the center of the target 30 radially outward at a constant rate. Any echoes received in the intervalbefore the next trigger pulse, are detected by the radar system 58 and applied to the terminal l10 of mixer 14. Iif no previous' signals have beenV stored or are circulating, a signal from the terminal is applied to the video amplifier 22V and thence through the switch 23 Atornoduate the writing beam byimeans Vof thefcontrol element 24. Preferably the frequency of low frequency oscillator 35 is of such a duration with, respectto the durationof a pulse emitted by theV radarsystem 58 (or Vof kan echo), that the switch 23 is in condition to apply the video amplifier 22 output to control element 24V at least partially, for any single echo. Accordingly, a charge is stored on the target 30 at a point radially deistant from the center at which the sweep is initiated yby an amount proportional to the range of the echoing object from the radar system 58. n

The antenna 60 is presumed in this instance to be of "the, type which is mechanically,r rotated azimuthally ywhereby' the azimuth of echoing ,objects may be Yde termined upon receipt of any echo. The deflection coils 29 beam Ymodulated by vthe signals from the video amplifier are connected to rotate at the same" angle fro'f some ducial position as the azimuthalangle ofthe antenna 60. Accordingly, the deflection coils 29 cause the radial deflection of the electron beam to be at the same angle from some predetermined radial line on the target 30 as the azimuthal angle of the antenna 60. Other means are known for controlling the sweeps of the two beams coordinated with the angle of the radiated energy from which the echo is received. These' means may .be diiferent from Vthe simple mechanical arrangement indicated here. Other types of display may also be employed;

As the electron beam advances across the strobe (radial n line), it is alternately advanced and retarded at the frequency of the low frequency oscillator 35. The alternate advance and retardation may be effected by superim-A posing the low frequency oscillation from oscillator 35 onto the signal applied from sweep generator 68 to the deflection coils 29. This is indicated by the connection between the low frequency oscillator 35'and the sweep generator68. V The deflection superimposed",upon.fthe

linear sweep need not be very great and infact is 'prefer ably of theorder otf 3 to 5 A,bearrrwidth at Atheztarget; 30.

' In each'advance of the electron,beam'acrossthestrobe; the low frequency oscillatorf 35 causes the, switch 23110 the grid 30a.

signal because of the modulation Asuperimposed bythe high frequency modulator 34, the; output Vof which'is then being applied tothe control element 24. ,Y

Such a signal being readrat the electrode 30C is img pressed across thetuned circuit of the inductor .50 and applied to the R. F.-amplier 52. There may befappree ciable capacitive coupling between the electrodex30c and sents an appreciable impedance between thelg'rid` 30a and ground. The resistor 56 is inserted forthe "same reason, that is, to prevent any short-circuiting.of.,the.j30 mc./s. modulated signal to ground through the lowfre: quency oscillator 35. The capacitor A48 on the other hand has a very'small capacity which presentsanfappre'. ciable impedance to the low frequency `signal from low frequency oscillator 35 but freely passes 'the 30 mc./s.

signal. The arrangement, in other words, is such asV to allow the application of suitable bias to' thegelectrode 30C, and also permitting the application of the low fre,- quency signal and exclusive reading by means of thehigh frequency signal.

The 30 mc./s. modulated signal whichlhas been applied to the R. F. amplifier 52 is demodulated in demodiilatoij 18, passed through the erase control 46 and thencedelay line 44 to return to the non-additive mixer 1 4. I

If no new signals are applied, the signals passtojithe video amplifier 22 andare rewritten. VMAt each Vbackvvai'icl v v step or retardation of the electron beam along the strobe line, the switch 23 applies the output of videoiarnpliiier 22 to control element 24. Also at these times thenlow frequency oscillator 35 is placing the electrode 30cat a potential to receive the signal being'written. N v

The delay time between the reading ofthe signal. pieked up from electrode 30e audits passage aroundihQflOQ However, such coupling does notgsliunt `the signal to ground/because of the R. F.' C. which pre- In each advance.V of theelectron beam e across the strobe, the low frequency oscillator 35 'causes .comprising the R. F. amplier 52, demodulator 18, erase .control 46, delay line 44, mixer 14, video amplifier f22 and back to the control element 24 of thestorage tube 28 should be equal as nearly as possible to the time required for the electron beam to travel from one reading point on a forward step until it next reaches the same point on a backward step. It is then apparent that any stored signals will be rewritten onrthe target at'substantially the same .points from which they were read.

The operation of the system of Fig. 1 may be more readily understood by reference to Fig. 2 in which there is! shown along the same time base idealized graphs `illustrating thesweep displacement, the potential of con- .trol element 24, and the potential of target electrode 30C. The sweep displacement may be considered iirst to have advanced a step at the greatest advance of which any stored signalis read as indicated by the legend Read (1). Du'ringthis interval oftime, `the control element 24 has applied to it a 30 mc./s. signal which is indicated conventionally as a high frequency ,p signal. The target electrode potential has `been broughtapproximately to zero volts s'o that thetarget is placed or actuated in condition to be read. A half period of the oscillations of low frequency oscillator later, the sweep displacement has stepped the beam backwards as indicated by the 2 legend Write (1). During this time one may presume a signal upon control element 24 from the video amplifier 22 as indicated by the positive-going pulse in the graph, which signal is therefore being stored. At the same time, the target electrode potential has been 'broughtito "-100 volts, the condition to which it was dition. The alternate advancement andlretardation of the electron beam'is indicated on the line X of Fig. 2 which may be taken as the strobe line, the circles indicating the dimensions of the electron beam at the point at which it `strikes the target. The electric wave or signal on the target electrode may be shaped as `shown before application to the target electrode.

The operation described in thepreceding paragraph is also illustrated in Fig. 2A. The strobe line is indicated on the target 30 in face view. The reading and writing areas and `the `sequence thereof are iillustrated on the strobe line X, but it will be understood that the areas are grossly exaggerated in order to be easily understood. In its travel along the strobe `line X outward, let it be supposedl that the beam is found in the portion of the area indicated read (l) at the point nearest the center O lof the target 30. As the beam moves outwardly along the strobe line X to the outermost limit to the read (l) area and-return, the `target is in a reading condition and the signal is read from the target. Next the beam sweeps quickly toward the center O until it reaches the outermost portion of the area indicated write (l) at which time the storage tube is in a writing condition and signals are written on the target along the strobe line X as the beam sweeps from the outer portion of the Write (l) area to the portion nearest the center O and out again. Next the beam is swept quickly to the read (2) area and reading is commenced as the beam reaches the innermost portion of the area indicated as read (2). The beam reads as it sweeps outwardly to the extreme radial position of the read (2) area and back again to the radially innermost portion. Then the beam is displaced quickly to the write (2) area, etc. The manner in which the reading and writing takes place with a single beam is fully apparent from a consideration of Figs. 2 and 2A.

In Fig. 3 a scheme of interlace scanning is schematically illustrated. According to this scheme, the spaces between the points to which the beam is stepped. on -one scan are utilized on the next scan. This enables the scanningrate to acquire the information for a complete PPI picture to `be cut in half. In other words, the `scan during one frame reads and writes on the elements which were omitted on` the previous frame. To accomplish this, it is only necessary to synchronize the sweep generator with `the trigger and the low frequency oscillator so `that throughout one scan, the beam starts from its initial central position on the radial sweep with. a step forward whereas on the next scan it starts with a step backwards. This may be accomplished by a mechanical connection 70 from the deflection coils 29 which reverses either `electronically or mechanically the phase of the application of the frequency oscillator 35 output tothe sweep generator 68 every time the deflection coils 29 complete a revolution. j l j In this system of the invention the problem of registration of the reading and writing information, that is, registration of the signals readto be rewritten upon the same points from which read is greatly improved' over prior systems, because a single electron beam is used for both functions and it will tend to remain upon the same strobe line as it is stepped back and forth. It may be `desirable to prevent reading or writing, or both, at or near one, or both, ofthe end points of each strobe or sweep line by suitable means known to the art, to prevent these end points from writing or reading spurioussignals. Such means are not illustrated. The steps should `be suciently large to prevent rewriting information on the target at the points from which it is being read. If it is desired to erase old information on the target, the erase `control 46 may be employed. This control interrupts the 'signal for a suitable period of time. The erasure can Ibe V,applied to 'all the old information or in a selected 4gate fashion to portions of the PPI stored signals.

What is claimed is:V i

l. In a signal storage system, the combination comprising alstorage tube having an electron beam gun and a storage target toward which said beam is directed, said target including signal `responsive means for actuating said target in one of a signal storing condition and signal `reading condition, and means comprising an oscillator to deflect said beam across said target in alternate forward and backward steps taken at the oscillator frequency, the forward steps being greater than the backward steps, said oscillator being also connected to said signal responsive means to actuate said target in response to the oscillator signals in a reading condition on each forward step and a storing condition on each `backward step.

2. The combination claimed in claim l, said electron gun comprising a control element to control the beam intensity in response to a signal applied thereto, a second oscillator of a higher frequency of oscillations than said first oscillator, means to make connection to a source of signals to be stored, and a switch connected to and under control of said oscillator and also connected to said high frequency oscillator and to said signal connection means to apply signals from said high frequency oscillator and from signal connection means alternately to said control element, said high frequency oscillator signal being applied to said control element at each beam forward step, and signals from said connecting means being applied to said control element at each beam backward step.

3. The combination claimed in claim 2, further comprising a circulating signal circuit connected to said storage target to read signals therefrom in said reading condition and connected to the said signal connection means as a source of the read signals, thereby completing a loop circuit, the time delay of signals from the reading thereof around the loop circuit to application to said control element being equal to the time for said beam after reaching a point an a forward step to next reach the same point on a backward step, whereby the signals read from Ione point are circulated and stored again at substantially jthe same pointV on thev said target. """"4.` The 'combination claimed in claim 3, said reading V*meanscomprising a tuned circuit connected to said target and responsive only to modulated signals of said thigh frequency oscillator, and a demodulator connected to said tuned circuit to demodulate said high frequency modulated signals.

5. The combination claimed in claim 4, said demodulator' being connected to said signal connection means through a mixer circuit including means to receive signals from a source external Vto the storage system, whereby external signals may be added to those circulating in the jsaid system.

6. The combination claimed in claim 3, further cornvprising an Aerasecontrol, connected between said target electrode and said control element to interrupt the application of signals.

"f'f/.gIn a'signal storage system the combination comprising a storage tube having an electronbeam gun, a vstorage target toward which the electron beam from said gun is directed, Vancl a signal receiving electrode, means to dee'ct said beam across said target, an oscillator havingy a firstfrequency of oscillation, a sweep generator connected to said deilecting means to control the beam deflection' in avsweep line across said target, a trigger generator circuit connected to said low frequency oscillator Vto produce a trigger signal at a submultiple of said `first frequencysaid sweep generator being connected to vsaid trigger generator to have the sweep frequency controlled at the said trigger frequency and connected to said voscillator to have superimposed on the said sweep deflection" the higher first frequency, thereby advancing the beam in forward and backward steps across said line on Vthe target, said target including an electrode, and means backward step of said beam to cause said signals to be i `read at' each forward step of said beam.

4' 8. In a signal storage system the combination comprising a storage tube having an electron beam gun, a control element to control the beam intensity, a storage target toward which said beam is directed, said target comprising a dielectric storage plate, a grid closely spaced from said plate between said plate and said gun, and an electrode on the side of said plateV away from said gun, an oscillator of a rst frequencyof oscillation, a trigger circuit connected to said oscillator to produce a trigger vvoltage at a submultiple of said'frst frequencya sweep generator connected to said trigger circuit and to said oscillator to generate a beam deflection electric wave of the trigger frequency and with the rst frequency superimposedthereon, a deflection means connected to said sweep generator to deflect said beam in response to said beam deflection wave, whereby the beam is deflected to vadvance in steps forward and backward across a line onsaid targetthe forward steps beingl greater than the quency andv signals from said source from said signal receiving means, said target electrode'being connected to said first oscillator to be at a higher readingora lower writing potentialrespectively during thev beam forward and backward steps while said switch respectively applies said second 4frequency and said signal to said control element, and a filter circuitv connected to said target electrode to receive second frequency modulated signals and reject those of other frequencies.

9. The system claimed in claim 8, further comprising a demodulatorconnected to said filter circuitto demodulate said modulated high-frequency signals, a mixer to receive said'demodulated signals, said signal applying means being connected to pass signals received fromsaid mixer, the time delay of thecircuit from ysaid target electrode throug'hrsaidfilter, demodulator mixer and signal apply.-

ingY means being,equalsubstantially to the time required therebyto interlace the forwardY and backwardpsteps to fall at different points on said target ori alternatesweeps alongthe sameline. a i

" 1l AV signal zstorage4 system comprising,V VanY electrical i storage tube having means for producing an electron beam, a beam'jcontrol'electrodegand a storage electrode toward which saidbeam is directed, means for applying elec- 4trical `signals to 'said/control electrode for modulating said electron. beam ,to store said signals on said storage electrode, means including an oscillator for deecting said electron beam acrosssaid storage electrode lin alternate forward and backward stepsat the frequency :of said oscillator,rneans for withdrawing from said tube on each forward step of said beam signals stored on said storage electrode, and means for re-storingsaid withdrawn signals on each backward step of said beamv at the same point on said storage electrode from which said signals were withdrawn..

References Cited inthe file of this patentV UNITED STATES PATENTS l A 2,059,004 Y LeedS 2--.. Oel. 27,1936 2,093,157 Nakashima et al Sept. 14, V1937 2,276,359 Von Ardenne Mai.:17,.` 1942 2,617,963 Arditi NOV. 11, 197'52 2,642,550 Williams June A16,1953

Williams Mar. 9,11954 

